Improve blog post date parsing

Previously the parsed date was automatically fomratted as UTC resulting
in a added time of 00:00:00.000+0000 which conflicts with the way the
date will be rendered through the UI.
This commit changes the date to only use the "pure" date format
(yyyy-MM-dd) without including any time and zone information.

GH-129

.gatsby/onCreateNode.js

@@ -15,18 +15,17 @@ const { ROUTE_BLOG, ROUTE_DOCS } = require("../src/config/routes/mappings");
 
 /**
  * Extracts the date of a blog post from the given path using the `REGEX_BLOG_POST_DATE` regular expression.
- * Note that the returned date is in UTC format to be independent of the time zone. The exact time of the day will be
- * parsed from the blog posts frontmatter "publishTime" field.
+ * The exact time of the day will be parsed from the blog posts frontmatter "publishTime" field.
  *
  * @private
- * @method extractDateFromPath
+ * @method extractBlogPostDateFromPath
  * @param  {string} path The path from which the blog post date should be extracted.
- * @return {string|null} The extracted blog post date in UTC format as JSON string if the given path matches the
- * regular expression, `null` otherwise.
+ * @return {string|null} The extracted blog post date if the given path matches the regular expression,
+ * `null` otherwise.
  */
 const extractBlogPostDateFromPath = path => {
   const date = REGEX_BLOG_POST_DATE.exec(path);
-  return date ? new Date(Date.UTC(date[1], date[2] - 1, date[3])).toJSON() : null;
+  return date ? `${date[1]}-${date[2]}-${date[3]}` : null;
 };
 
 /**
@@ -64,7 +63,7 @@ const onCreateNode = ({ node, getNode, actions }) => {
       createNodeField({
         node,
         name: `${nodeFields.date.name}`,
-        value: extractBlogPostDateFromPath(relativePath)
+        value: date
       });
       createNodeField({
         node,

src/config/project/constants.js

@@ -25,13 +25,13 @@ import { getSemVerFromGitDescribe } from "utils";
 const COPYRIGHT_YEAR = new Date().getFullYear();
 
 /**
- * The date format for the "date-fns" library according to ISO 8601.
+ * The date format for the [date-fns](https://date-fns.org) library according to ISO 8601.
  *
  * @constant {string}
  * @see https://date-fns.org/v1.29.0/docs/format
  * @see https://en.wikipedia.org/wiki/ISO_8601
  */
-const DATE_FORMAT = "yyyy-MM-ddTHH:mm:ssxx";
+const DATE_FORMAT = "yyyy-MM-dd'T'HH:mm:ssxx";
 
 /**
  * The name of the current Git branch extracted from the local Git repository.

src/data/graphql/fragments.js

@@ -77,17 +77,12 @@ export const gqlFragmentContentDocsPageFrontmatter = graphql`
 
 /**
  * GraphQL fragment for the node fields of an MDX blog post.
- * Gatsby internally relies on Moment.js for the provided `formatString` function.
- * The allowed tokens can be found in the official Moment.js documentation.
- *
- * @see https://momentjs.com/docs/#/displaying/format
- * @see https://www.gatsbyjs.org/docs/graphql-reference/#format
  */
 export const gqlFragmentContentBlogPostFields = graphql`
   fragment contentBlogPostFields on Mdx {
     fields {
       contentSourceType
-      date(formatString: "YYYY-MM-DDTHH:MM:ssZZ")
+      date
       relativeDirectory
       slug
       slugParentRoute